The present invention relates to a hardness testing apparatus in which a hardness of a sample is measured by forming a dimple on the surface of the sample.
In a first earlier development, a hardness testing apparatus is used. In this apparatus, a load is applied to the surface of a sample by an indenter to form a dimple on the surface of the sample, and a hardness of the sample is measured.
For example, a hardness testing apparatus 500 shown in FIG. 25 is known (for example, refer to FIG. 2 of Published Japanese Patent Application (Tokkaihei) No. H10-132722).
As shown in FIG. 25, the hardness testing apparatus 500 has an indenter shaft unit 510 having an indenter shaft 502 and a load applying mechanism 530 for applying a predetermined load to the indenter shaft 502. An indenter 501 is arranged on the top of the indenter shaft 502 to form a dimple in a sample S mounted on a sample stand 555.
The indenter shaft unit 510 is placed above the sample stand 555 and has a supporting frame 503 arranged on a body (not shown) of the testing apparatus 500, a supporting spring 504 arranged on an indenter shaft support 503a which stands on the supporting frame 503, a motion plate 507 elastically supported by the supporting frame 503 through a plate spring 505 and a return spring 506, a push bar 508 arranged on the supporting frame 503 so as to be movable in the upper and lower directions, the indenter shaft 502 and the like. A lower end 508a of the push bar 508 comes in contact with an external end 507b of the motion plate 507. An upper end 502a of the indenter shaft 502 is attached to the supporting spring 504, and a contact member 502b of the indenter shaft 502 is supported by a shaft receiver 507a of the motion plate 507 placed below the indenter shaft 502.
The load applying mechanism 530 has a dead weight member 570 arranged above the indenter shaft unit 510 and a control lever 520.
The control lever 520 is supported by a rotational shaft 521 at the almost center of the control lever 520 so as to rotate around the body of the testing apparatus. A pressing member 522 is arranged on one end 520a of the control lever 520 to push down the upper end of the pushing bar 508 of the indenter shaft unit 510. A roller 524 being rotatably contacted with an eccentric cam 523 is attached to the other end 520b of the control lever 520. The control lever 520 extends from the rotational shaft 521 toward a position above the indenter shaft unit 510 and extends above the indenter shaft 502, and the end 520a of the control lever 520 pushes down the pushing bar 508 at an upper position of the pushing bar 508. A hole 520c extending in the vertical direction is formed in the control lever 520 at a position placed above the indenter shaft 502 of the control lever 520.
The dead weight member 570 has a plurality of dead weights 571, a load shaft 572 vertically extending in the center of the dead weight member 570, and a casing 573 covering the dead weights 571. A lower portion of the load shaft 572 penetrates through the hole 520c of the control lever 520 and extends downward, and a lower end 572a of the load shaft 572 is arranged so as to be opposite to an upper end 502a of the indenter shaft 502. A pin 574 projects from the load shaft 572 and comes in contact with the control lever 520 from its upper side.
In the above configuration of the hardness testing apparatus 500, the control lever 520 is rotated with the rotation of the eccentric cam 523 to push down the push bar 508 of the indenter shaft unit 510 or to release the push-down of the push bar 508. When the push bar 508 is pushed down, the supporting frame 503 (motion plate 507) is pushed down. The control lever 520 lowers the position of the dead weight member 570 to apply a predetermined load to the indenter shaft 502.
When the hardness test is performed by using the hardness testing apparatus 500, the sample S is mounted on the sample stand 555 placed below the indenter shaft 502 in the body of the hardness testing apparatus 500, and the position of the indenter shaft 502 is lowered by rotating the eccentric cam 523 and lowering the position of the dead weight member 570. When the position of the indenter shaft 502 is lowered so as to make the top of the indenter 501 come in contact with the sample S, the indenter shaft 502 is released from the shaft receiver 507a of the motion plate 507. Thereafter, the dead weight member 570 applies a predetermined load (weight of the dead weights 571; test force, for example, from almost 98 mN to 20N) to the indenter shaft 502, and a dimple is formed in the sample S by the indenter 501. After formation of the dimple, the control lever 520 is rotated in the direction reverse to that in the formation of the dimple to heighten the position of the supporting frame 503 (motion plate 507) and to move the indenter shaft 502 upward, and the indenter shaft 502 departs from the sample S. Therefore, the size of the dimple or the like is measured by observing the dimple formed in the sample S with a microscope (not shown) or the like, and a hardness of the sample S is determined.
However, in case of the Application No. H10-132722, when the test force is output from the dead weights 571 of the dead weight member 570 arranged in the hardness testing apparatus 500 so as to make the hardness testing apparatus 500 form the dimple in the sample S, a problem arises in that a repulsion force of both the supporting spring 504 and the return spring 506 elastically supporting the indenter shaft 502 acts to deaden the test force.
That is, in the hardness testing apparatus 500, the action force (repulsion force) influences the test force output based on the dead weights 571 of the dead weight member 570, and the hardness test is performed at a test force slightly different from the substantial test force.
Further, in the case of Application No. H10-132722, because the test force required to form the dimple in the sample S is output by the dead weight member 570 of the hardness testing apparatus 500, the test force is discretely output according to each dead weight 571 in the range based on the dead weights 571 of the dead weight member 570.
In a second earlier development, in a hardness testing apparatus 540 schematically shown in FIG. 26A, an indenter shaft 544 having an indenter 543 at the top thereof is elastically supported to a body 542 of the testing apparatus through supporting springs 545. A predetermined force F is applied to the indenter shaft 544 in its axial direction to push the indenter 543 to a sample, and a dimple is formed in the sample. A hardness of the sample is measured according to the shape of the dimple (for example, refer to Published Japanese Patent Application (Tokkaihei) No. H11-37915).
However, in the case of Application No. H11-37915, as shown in FIG. 26A, even though the force F is applied to the indenter shaft 544 in its axial direction, the shaft axis of the indenter shaft 544 sometimes slightly deviates in a direction perpendicular to the axial direction of the indenter shaft 544 because of warps of the supporting springs 545. When the shaft axis of the indenter shaft 544 deviates, as shown in FIG. 26B, flaws generated by the dragging of the indenter 543 along the surface of the sample are sometimes formed in the dimple. Therefore, the flaws sometimes prevent the correct recognition of the shape of the dimple, and a problem arises in that a hardness of the sample sometimes cannot be measured with high accuracy.
In a third earlier development, a hardness testing apparatus disclosed in Published Japanese Patent Application (Tokkai) No. 2003-161684 has an indenter supporting bar having an indenter at the top thereof, a supporting mechanism for movably supporting the indenter supporting bar, and an actuator for driving the indenter supporting bar in its axial direction.
The supporting mechanism has two plate springs supporting the top and bottom of the indenter supporting bar respectively and formed in an E shape. The plate springs are arranged at upper and lower positions of the indenter supporting bar respectively and extend parallel to each other in the same direction as each other. Open ends of both side spring portions in each plate spring are fixed to a fixed frame, and an open end of the central spring portion each plate spring is fixed to the indenter supporting bar supporting the indenter.
When a predetermined force is applied to the indenter supporting bar in an axial direction the indenter supporting bar, the side spring portions and the central spring portions of the plate springs are deformed. Circular motions of the side spring portions and the central spring portions in the plate springs arranged in parallel to each other cancel each other out with the deformation of the plate springs, and the indenter supporting bar can straight move. Therefore, the indenter always faces the surface of the sample without changing the direction of the indenter, and the indenter performs only straight movement.
However, in the above-described configuration of the supporting mechanism, when the moving speed of the indenter supporting bar is increased, the indenter supporting bar vibrates at its characteristic frequency due to the action force applied from the actuator to the indenter supporting bar, and the indenter violently collides with the sample. Therefore, a problem arises in that a hardness of the sample is erroneously measured.
Further, when the indenter supporting bar vibrates due to disturbance, the indenter supporting bar vibrates in the upper and lower directions at its characteristic frequency. As a result, the load applied to the sample is changed due to the influence of vibration of disturbance. Therefore, another problem arises in that a hardness of the sample is erroneously measured in the test of a low hardness of a film or the like.
Moreover, when the force is applied to the indenter supporting bar, the two upper and lower plate springs are independently moved. Therefore, the indenter supporting bar slightly deviates in the direction perpendicular to the axial direction of the bar, and the dimple formed by the indenter is deformed. As a result, another problem arises in that a hardness of the sample is erroneously measured.
In the hardness testing apparatus disclosed in Application No. 2003-161684, when the two upper and lower plate springs composing the supporting mechanism are connected to each other by a connecting member, movement of indenter supporting bar further can be made straight in the axial direction of the bar.
However, in this hardness testing apparatus, when the indenter reaches the surface of the sample while applying a predetermined force to the indenter supporting bar, the two plate springs are further warped as compared with in the before-test of the hardness.
Therefore, when vibration of disturbance occurs in the connecting member of the plate springs, the indenter supporting bar sometimes slightly deviates in the direction perpendicular to the axial direction of the bar, and the dimple formed by the indenter is deformed. Therefore, a problem arises in that a hardness of the sample is erroneously measured.
In a fourth earlier development, Vickers hardness testing apparatus is known as a hardness testing apparatus (for example, refer to Published Japanese Patent Application (Tokkai) No. 2000-292333). In this apparatus, the size (for example, length between predetermined points of dimple (length of diagonal line)) of a dimple formed by pushing an indenter to a sample at a predetermined force is measured, and a hardness of the sample is calculated. The Vickers hardness testing apparatus has an indenter for forming the dimple in the sample and an objective lens for displaying an enlarged image of the dimple formed by the indenter on a monitor. Normally, a plurality of objective lenses are prepared to measure dimples having various sizes.
When a user daily performs the hardness test of a fixed type of sample, it is easy to assume a hardness of the sample by user's experience. Therefore, the user determines an optimum objective lens according to information relating to the size of the dimple, a test force is set by user's experience to push the indenter to the sample according to the assumed hardness of the sample, and the hardness test is performed.
In the Vickers hardness testing apparatus of Application No. 2000-292333, to display the image of the dimple at its optimum size on the monitor, it is required to select an objective lens having a magnification optimum to the size of the dimple. However, because the selection of the objective lens based on the size of the dimple is performed by user's experience, the user requires a certain degree of skill.
Further, when the test force set by user's experience is not appropriate, a dimple having a size considerably far from the expected size is formed in the sample. Therefore, the image of the dimple cannot be displayed at the optimum size on the monitor, and a problem arises in that the hardness test cannot be accurately performed.